They really didn't actively think it was a good idea. They changed the discovery tab to be a web page, which as the github repo linked by the OP will show you, is now handled in the same repo (by the same people) as the AMO website proper.

It was a mistake, and not as huge of one as people are making it out to be. As they have repeatedly pointed out, their GA contract makes it essentially a non-issue, unless you believe Google is so obsessed with tracking that they will violate their contract with Mozilla.

I disagree. I think people who believe in protecting their privacy can also be OK with Google Analytics processing, anonymizing, and aggregating the data. I also understand why someone would not feel that way. I think it's something about which reasonable people can disagree. This is why Mozilla provides the option[1].

[1] Which is, incorrectly, not being respected. This is a bug which they will fix.